sedimentary
Oolite (Ooids)
Oolitic Limestone (Principal mineral: Calcite, CaCO3)
AI-generated identification · may be incorrectHardness: 3 (Mohs scale); Color: Typically white, gray, or tan; Luster: Dull to pearly; Structure: Spherical or subspherical grains (ooids) usually <2mm in diameter; Cleavage: Perfect rhombohedral in individual crystals but not visible in the aggregate shell.
- Hardness
- 3 (Mohs scale)
- Color
- Typically white, gray, or tan
- Luster
- Dull to pearly
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Physical properties
Hardness: 3 (Mohs scale); Color: Typically white, gray, or tan; Luster: Dull to pearly; Structure: Spherical or subspherical grains (ooids) usually <2mm in diameter; Cleavage: Perfect rhombohedral in individual crystals but not visible in the aggregate shell.
Formation & geological history
Formed in warm, supersaturated, shallow marine waters. Ooids develop as concentric layers of calcium carbonate precipitate around a nucleus (like a sand grain or shell fragment) while being rolled by wave action. Most commonly found in strata from the Jurassic, Mississippian, and Holocene eras.
Uses & applications
Used as high-quality building stone (e.g., Portland stone), in the manufacture of lime and cement, as a flux in steel production, and sometimes as an aggregate in road construction.
Geological facts
The name comes from the Greek word 'oion' for egg, because the rock resembles fish roe. Famous examples include the 'Indiana Limestone' used in the Empire State Building and the Pentagon.
Field identification & locations
Field identification involves looking for small, egg-shaped grains that react with dilute hydrochloric acid (fizzing). They are commonly found in high-energy coastal environments like the Great Bahama Bank or the Great Salt Lake.
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